360 DISCOVERY REPORTS 



of pregnancy which was 19 cm. in diameter lacked a cavity. Conversely, cavities are found in the 

 much smaller corpora lutea of other animals; in man, for instance, corpora lutea of pregnancy or 

 ovulation less than 1 cm. in diameter commonly have cavities (Dubreuil and Riviere, 1947) and vesi- 

 cular corpora lutea are relatively common in the cow (Hammond, 1927). These observations mean 

 that the hypothesis of vascular limitation is untenable. 



Secretion of fluid by the follicle wall continues for an appreciable time after ovulation and vesicular 

 corpora lutea in other mammals are usually attributed to the continued secretion of liquor folliculi by 

 the ruptured follicle after the aperture has become closed (Brambell, 1956, p. 474). According to 

 Robinson (1918) the persistence of the central cavity in the ferret depends on the degree of separation 

 of the internal limiting membrane at ovulation. The point of rupture of the follicle is closed by a 

 tenacious coagulum, the tertiary liquor folliculi, which also redistends the collapsed follicle often to 

 the size it originally was before ovulation (Harrison, 1948). 



9 10 11 u 13 



CL. DIAMETER IN CMS. 



9 10 II \2 



CL DIAMETER IN CMS 



Text-fig. 9. a, Relation between cavity diameter and corpus luteum diameter, b, Relation between corpus 



luteum size and the incidence of cavities. 



The appearance of fin-whale corpora lutea of the vesicular type suggests that they are usually formed 

 in this way. In most corpora with large cavities (Text-fig. 5 h-k) the stigma is inconspicuous and there 

 is no eversion of luteal tissue to form a corona. This suggests that the aperture became closed again 

 after ovulation and remained closed. The corpus illustrated in Text-fig. $k has a small stigma, but 

 the corpus has a distended appearance and the luteal tissue has obviously been subjected to pressure 

 from inside, presumably by continued secretion of fluid. The most uncommon type of corpus (Text- 

 fig. 5 /) has an opening and a conspicuous corona. It immediately suggests that the aperture closed 

 after ovulation, but that the internal fluid pressure later forced it open when the corpus luteum had 

 almost attained its definitive size and form. 



There is a relation between the size of the corpus and the size of its cavity (Text-fig. ga). For 

 107 fin-whale corpora for which the cavity size is known the mean size of the cavity increases from 

 i-8 cm. at a corpus size of 7-8 cm., to 4-1 cm. at a corpus size of 14-15 cm. 



There is also a relationship between the size of the corpus luteum and the prevalence of the vesicular 

 type. For 701 corpora lutea, 120 of which have cavities, the percentage of vesicular corpora in suc- 

 cessive size groups increases from about 10% at a corpus size of 6-7 cm. to about 20% in corpora 

 above 13 cm. in diameter (Text-fig. gb). In other words the larger corpora show a greater tendency 

 to have cavities. Extrapolation suggests that corpora below 3-4 cm., forming from ruptured follicles, 

 would not be vesicular. The limited material available supports this. In Text-fig. 10 a number of small 

 accessory corpora lutea are illustrated and all which have central cavities are formed from unruptured 

 follicles. These accessory corpora lutea are produced in such limited numbers that they do not affect 

 the figure for the percentage of corpora with cavities. Corpora lutea of ovulation with a mean diameter 





